Hydrogeothermal Conditions in Éire - Geological Survey of Ireland

- 15 -•They merit only very brief discussion. For Silicon, it will be noted that1009 and 1001 lie well away from the main envelope showing Si increasingas temperature increases.; these are springs noticably high in Cl and TDS.The third spring of this little group, No. 1004, lies well within theenvelope. It is generally reported that the si of thermal waters isaffected by the TDS of such waters. For Iodine, there is only a very slighttendancy for I to increase as temperature increases. The points most offthe line of Fig. 5, are 2001 and 2002 (Mallow Spa), 1007 (st. Germans) and1001 (Louisa Bridge) . While it could be said that the I of the first threeof these was lower than might be expected, and that the I of No. 1001 ishigher than might be expected considering their temperatures, the basis forsuch an attribution is slight and weak. Further work on trace elementsis clearly required.(iii) Gases. In some of the springs, as Enfield and Mallow, anappreciable amount of gas is given off, bubling up through the waters.Its composition has not been determined, though the earlier work of Plunkett& Studdert (1883) is of interest. Generally, the gases are odourless,though a faint whiff of sulphur or hydrogenated sulphur is sometimesdetected; it may arise from decomposition of organic matter in the mud ofthe spring.(iv)Isotopes.As yet, there have been no isotope determinations.11-7. Main InferencesIt is considered of use to present here the 12 main inferenceswhich have been drawn with regard to these warm springs.LocationGeology~eophysicsHydrologyHydrothermalHydrochemical(i)(ii)(iii)(iv)(v)(vi)(vii)(viii)(ix)(x)(xi)Several occur on higher ground than might be expected.Some have been made functional by man's activities.The Leinster springs appear to be 8 km apart.All issue from Dinantian limestones, some 1,500 to2,500 m thick.Some small Tertiary intrusives have been reportedfrom their vicinity.Their occurrences can often be located with respectto fold structures.Certain gravity lows may have some connection withthese warm springs.Discharges increase in spring, as expected formeteoric waters under the hydrological cycle.Temperatures peak in spring, decline from May to Oct;they are irregular.Most of the warm springs show no abnormal hydrochemicalcharacteristics.High CI and TDS are restricted to three springs occurringalong a synclinal structure.(xii) There are faint indications that Si and I increase withincreasing temperature.